K2 + SignalLink: Setting gains for digital modes

[Chris Kimball]

I operate digital modes with the K2/KPA with a SignalLink computer interface.  The SignalLink drives the microphone input to the K2.  The K2 has compression turned off (1:1) and a mike gain of 3.  The SignalLink computer interface is at 100% gains on both sides and the SignalLink has the default internal gain jumpers.

I get occasional comments that I'm splattering, a very serious concern.  Unfortunately I lack instrumentation to study the problem.  

How should I set the audio (SignalLink) drive gain and the RF (K2 Power) drive? My normal operation is not smoke-producing, so this is not a duty-cycle question.

Thanks,

Chris
NQ8Z

[EricJ-2]

Can't help you with the specific problem as I use a RigBlaster instead
of the SignaLink. But a means to monitor your signal quality is pretty
basic and the solution is simple.

I have both the PSKMeter (~$45 kit) and the KK7UQ IMD Meter (~$150
assembled). Both do a great job. Both can be "online" at all times to
monitor PSK31 and PSK63. I find that IMD levels change using the K2
depending on band to some extent and things get bumped, so I don't like
to just set-and-forget. Both meters agree fairly closely when I've used
them simultaneously.

The PSKMeter requires inserting a BNC T-connector at the output of the
K2. This is used to couple a sample of the outgoing rf signal to the
meter. The meter connects to a serial port on your computer for display
of results.

http://www.ssiserver.com/info/pskmeter/

The IMD Meter is self sufficient. No connections to the rig or computer;
a small antenna picks up your transmitted signal. Results read out on a
small LED display. It doubles as a field strength meter. With no
connections, it's always ready for whichever rig I fire up (K2, PSK-20,
Softrock Xcvr)

http://kk7uq.com/html/imdmeter.html

There are probably other easy ways available, but I think it should be
basic equipment in a PSK shack.

Eric
KE6US

On 4/14/2013 9:25 AM, Chris Kimball wrote:

> I operate digital modes with the K2/KPA with a SignalLink computer interface.
> The SignalLink drives the microphone input to the K2.  The K2 has
> compression turned off (1:1) and a mike gain of 3.  The SignalLink computer
> interface is at 100% gains on both sides and the SignalLink has the default
> internal gain jumpers.
>
> I get occasional comments that I'm splattering, a very serious concern.
> Unfortunately I lack instrumentation to study the problem.
>
> How should I set the audio (SignalLink) drive gain and the RF (K2 Power)
> drive? My normal operation is not smoke-producing, so this is not a
> duty-cycle question.
>
> Thanks,
>
> Chris
> NQ8Z
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-SignalLink-Setting-gains-for-digital-modes-tp7572576.html
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[KC6CNN]

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[Don Wilhelm-4]

Chris,

For data modes with the K2, there is an indication in the K2 itself that
should prevent splattering.  That is the ALC meter.
Turn the RF/ALC meter to read ALC, then adjust your audio level until
you see the LED display blinking the 10th bar of the LED indicator -
then back off the gain a bit until that 10th LED flickering goes away.  
At that point, your audio level is correct.

Now adjust the power knob to your desired power output level and operate.

I do suggest that you set up the RTTY filter set and use those filters
for data modes because the SSBC menu item is independent of the SSB
setting.  Set SSBCr to 1:1 (the SSBC parameter for SSB can be set to
anything desired for voice).  That will assure that you have compression
turned off for data modes.

73,
Don W3FPR
On 4/14/2013 12:25 PM, Chris Kimball wrote:

> I operate digital modes with the K2/KPA with a SignalLink computer interface.
> The SignalLink drives the microphone input to the K2.  The K2 has
> compression turned off (1:1) and a mike gain of 3.  The SignalLink computer
> interface is at 100% gains on both sides and the SignalLink has the default
> internal gain jumpers.
>
> I get occasional comments that I'm splattering, a very serious concern.
> Unfortunately I lack instrumentation to study the problem.
>
> How should I set the audio (SignalLink) drive gain and the RF (K2 Power)
> drive? My normal operation is not smoke-producing, so this is not a
> duty-cycle question.
>
> Thanks,
>
>

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[Chris Kimball]

Thanks, Don!

I never knew quite what the ALC was for.  Good point about the RTTY filter set, too.

Chris
NQ8Z

[Chris Kimball]

Thanks for the comments.

I'm using Olivia/Contestia most of the time rather than MPSK.  The possible splatter is with the SignalLink gains at 9 o'clock, a near minimal setting.  Aside from the transmit gains, the system is operating normally, and the sound card is clearly recognized and in use.  The sound card gains are maximized just to take them out of the picture.

I don't always get comments about splattering, by the way.  My fear is that folks are to kind to point it out!

Chris,
NQ8Z

[KC6CNN]

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[Don Wilhelm-4]

Chris,

With your soundcard gains at maximum, it is possible that the output is
being overdriven and causing distortion (they are not "out of the
picture" at all.
I suggest you reduce the soundcard gain to the range of 1/2 to 2/3 of
full which will allow more range on the SignaLink gain.

73,
Don W3FPR

On 4/14/2013 2:40 PM, Chris Kimball wrote:
>
> Thanks for the comments.
>
> I'm using Olivia/Contestia most of the time rather than MPSK.  The possible
> splatter is with the SignalLink gains at 9 o'clock, a near minimal setting.
> Aside from the transmit gains, the system is operating normally, and the
> sound card is clearly recognized and in use.  The sound card gains are
> maximized just to take them out of the picture.
>

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[Bill Coleman-2]

On Apr 14, 2013, at 12:25 PM, Chris Kimball <[hidden email]> wrote:

> I operate digital modes with the K2/KPA with a SignalLink computer interface.
> The SignalLink drives the microphone input to the K2.  The K2 has
> compression turned off (1:1) and a mike gain of 3.  The SignalLink computer
> interface is at 100% gains on both sides and the SignalLink has the default
> internal gain jumpers.
>
> I get occasional comments that I'm splattering, a very serious concern.
> Unfortunately I lack instrumentation to study the problem.

You have to adjust the gain as you change bands. Unfortunately the K2 gain profile varies wildly from band to band. Either adjust until you just barely get any ALC indication, or adjust until you just barely get the requested power out.

>  How should I set the audio (SignalLink) drive gain and the RF (K2 Power)
> drive? My normal operation is not smoke-producing, so this is not a
> duty-cycle question.

Set the K2 power level at whatever power you desire. Then increase the audio level until you just barely make that power level. You should be pretty close to just barely having ALC action.

When you change bands, do it again.

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
           -- Wilbur Wright, 1901

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[Jim Brown-10]

On 4/14/2013 12:15 PM, Don Wilhelm wrote:
> I suggest you reduce the soundcard gain to the range of 1/2 to 2/3 of
> full which will allow more range on the SignaLink gain.

YES!  Several times I've published a simple procedure for setting
computer sound card levels.  It goes like this.

1) Find "cliip level" on the sound card. To do this, feed the sound card
output to a scope, get your RTTY or PSK program going, and push the
buttons that cause it to send tones to the radio. On the scope,
gradually increase the sound card output slider until you see squaring
at the top and bottom of the sine wave.

If you don't have a scope handy, listen on headphones as you gradually
increase the level until you hear the tones get "raspy" or "harsh" or
"brighter." With an AC voltmeter, look for the point when the reading no
longer increases as you increase the slider.  Of these three methods,  
the scope is best, your ears and headphones are second best. Use the
voltmeter method only if your hearing is gone and you don't have a scope.

2) Now that you've established "clip level," back off the slider by 6
-10 dB.  6 dB is half the voltage, 10 dB is about one-third the voltage,
easy to see on a scope or voltmeter. If you're using your ears, back off
the slider until it SOUNDS "half as loud." This works because human
hearing is logarithmic, and a reduction in level is HEARD as "half as
loud." The reason we go 6-10 dB below clip is that distortion in cheap
audio stages starts rising in the range of 6 dB below clip, so we make
our signals cleaner if we back it off by that 6-10 dB.  .

This procedure works for ALL audio output stages and all radios, and is
not limited to Signal Link (which, by the way, is not that great a sound
card).

This procedure sets the level for the computer output. You still need to
follow instructions in the K3 (or KX3) manual to set levels in the radio
itself.

73, Jim Brown K9YC
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[Don Wilhelm-4]

Yes, the K2 transmit gain can change with the various bands.  There is
some level of TX RF gain compensation in the K2 circuits, but it is not
perfect.

Because of the way the K2 controls power, setting the power first and
then bringing up the audio to produce that power output is a bit
"iffy".  Adjusting the audio for no ALC indication as I stated earlier
and then adjusting the power knob will always work.

Explanation -- The K2 tries to adjust the power output to produce the
requested power in all cases.  If the audio input is too low, the K2
measures the RF power output, then compares it to the requested power -
the MCU will increase the power in an attempt to bring up the output
power - your audio will still be low at that point, the K2 will increase
the drive, and then when you subsequently increase the audio level, the
power will overshoot the requested power, and then has to do the process
over again to bring the power down.  The result is that there are often
complaints about "power creep" when using digital modes.

For best results, adjust the audio level first for full audio but no
ALC, then adjust the power knob.

73,
Don W3FPR


On 4/14/2013 3:23 PM, Bill Coleman wrote:

> On Apr 14, 2013, at 12:25 PM, Chris Kimball <[hidden email]> wrote:
>
>> I operate digital modes with the K2/KPA with a SignalLink computer interface.
>> The SignalLink drives the microphone input to the K2.  The K2 has
>> compression turned off (1:1) and a mike gain of 3.  The SignalLink computer
>> interface is at 100% gains on both sides and the SignalLink has the default
>> internal gain jumpers.
>>
>> I get occasional comments that I'm splattering, a very serious concern.
>> Unfortunately I lack instrumentation to study the problem.
> You have to adjust the gain as you change bands. Unfortunately the K2 gain profile varies wildly from band to band. Either adjust until you just barely get any ALC indication, or adjust until you just barely get the requested power out.
>
>>   How should I set the audio (SignalLink) drive gain and the RF (K2 Power)
>> drive? My normal operation is not smoke-producing, so this is not a
>> duty-cycle question.
> Set the K2 power level at whatever power you desire. Then increase the audio level until you just barely make that power level. You should be pretty close to just barely having ALC action.
>
> When you change bands, do it again.
>

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[Chris Kimball]

I've been playing with this for the the last few hours.

It's possible to reduce the input level to get the 10-th ALC bar to disappear and, apparently, provide too little signal to the RF amp.  It seems a little sensitive on the SignalLink Tx gain control.

Given that I'm at the low end of the gain for a single ALC bar indication, am I likely to be overloading?  In other words, is a single ALC bar acceptable if it's at the low end of the Tx gain setting?  

I am going to 50% gain on both sound card levels.

Chris
NQ8Z

[KC6CNN]

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